Interlaced multiband antenna arrays

ABSTRACT

Antenna arrays which can work simultaneously in various frequency bands thanks to the physical disposition of the elements which constitute them, and also the multiband behavior of some elements situated strategically in the array. The configuration of the array is described based on the juxtaposition or interleaving of various conventional mono-band arrays working in the different bands of interest. In those positions in which elements of different multiband arrays come together, a multiband antenna is employed which covers the different working frequency bands. The advantages with respect to the classic configuration of using one array for each frequency band are: saving in cost of the global radiating system and its installation (one array replaces several), and its size and visual and environmental impact are reduced in the case of base stations and repeater stations for communication systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 13/530,249, filed on Jun. 22, 2012. U.S. patent applicationSer. No. 13/530,249 is a continuation of U.S. patent application Ser.No. 13/044,831, filed on Mar. 10, 2011 and which is now U.S. Pat. No.8,228,256. U.S. patent application Ser. No. 13/044,831 is a continuationof U.S. patent application Ser. No. 12/476,308, filed on Jun. 2, 2009and which is now U.S. Pat. No. 7,932,870. U.S. patent application Ser.No. 12/476,308 is a continuation of U.S. patent application Ser. No.11/803,782 which is now U.S. Pat. No. 7,557,768, issued on Jul. 7, 2009.U.S. Pat. No. 7,557,768 is a continuation of U.S. patent applicationSer. No. 10/988,261 which is now U.S. Pat. No. 7,250,918, issued on Jul.31, 2007. U.S. Pat. No. 7,250,918 is a continuation of U.S. patentapplication Ser. No. 10/135,019 which is now U.S. Pat. No. 6,937,191,issued on Aug. 30, 2005. U.S. Pat. No. 6,937,191 is a continuation ofPCT/ES99/00343, filed on Oct. 26, 1999. U.S. patent application Ser. No.13/530,249, U.S. Pat. No. 8,228,256, U.S. Pat. No. 7,932,870, U.S. Pat.No. 7,557,768, U.S. Pat. No. 7,250,918, U.S. Pat. No. 6,937,191 andInternational Application No. PCT/ES99/00343 are incorporated herein byreference.

OBJECT OF THE INVENTION

The present invention consists of antenna arrays which can be operatedsimultaneously in various frequency bands thanks to the physicaldisposition of the elements that constitute it, as well as the multibandbehaviour of some elements situated strategically in the array.

The array configuration is described on a basis of the juxtaposition orinterleaving of various conventional single-band arrays operating in thedifferent bands of interest. In those positions where elements ofdifferent multiband arrays come together, use is made of a multibandantenna which covers the different working frequency bands.

The use of a multiband interleaved antenna array (hereinafter simplyMultiband Interleaved Array, MIA) implies a great advantage over theclassical solution of employing an array for each frequency band: thereis a cost saving in the overall radiating system and in its installation(one array replaces several), its size is reduced as well as its visualand environmental impact in the case of base and repeater stations forcommunication systems.

The present invention finds its application in the field oftelecommunications and more specifically in radiocommunication systems.

BACKGROUND AND SUMMARY OF THE INVENTION

Antennas started to be developed at the end of the nineteenth centurybased on the fundamental laws of electromagnetism postulated by JamesClerk Maxwell in 1864. The invention of the first antenna has to beattributed to Heinrich Hertz in 1886 who demonstrated the transmissionthrough air of electromagnetic waves. In the mid-1940's the fundamentalrestrictions regarding the reduction in size of antennas were shown withrespect to wavelength and at the beginning of the sixties appeared thefirst frequency-independent antennas (E. C. Jordan, G. A. Deschamps, J.D. Dyson, P. E. Mayes, “Developments in Broadband Antennas,” IEEESpectrum, vol. 1, pp. 58-71, April 1964; V. H. Rumsey,Frequency-Independent Antennas. New York Academic, 1966; R. L. Carrel,“Analysis and design of the log-periodic dipole array,” Tech. Rep. 52,Univ. of Illinois Antenna Lab., Contract AF33 (616)-6079, October 1961;P. E. Mayes, “Frequency Independent Antennas and Broad-Band DerivativesThereof”, Proc. IEEE, vol. 80, no. 1, January 1992). At that timeproposals were made for helical, spiral, log-periodic arrays, cones andstructures defined exclusively by angle pieces for the implementation ofbroadband antennas.

Antenna array theory goes back to the works of Shelkunoff (S. A.Schellkunhoff, “A Mathematical Theory of Linear Arrays,” Bell SystemTechnical Journal, 22,80), among other classic treatises on antennatheory. Said theory establishes the basic design rules for shaping theradiation properties of the array (principally its radiation pattern),though its application is restricted mainly to the case of mono-bandarrays. The cause of said restriction lies in the frequency behaviour ofthe array being highly dependent on the ratio between the distancebetween elements (antennas) of the array and the working wavelength.Said spacing between elements is usually constant and preferably lessthan one wavelength in order to prevent the appearance of diffractionlobes. This implies that once the spacing between elements is fixed, theoperating frequency (and the corresponding wavelength) is also fixed, itbeing particularly difficult that the same array work simultaneously atanother higher frequency, given that in that case the magnitude of thewavelength is less than the spacing between elements.

The log-periodic arrays suppose one of the first examples of antennaarrays capable of covering a broad range of frequencies (V. H. Rumsey,Frequency-Independent Antennas. New York Academic, 1966; R. L. Carrel,“Analysis and design of the log-periodic dipole array,” Tech. Rep. 52,Univ. Illinois Antenna Lab., Contract AF33 (616)-6079, October 1961; P.E. Mayes, “Frequency Independent Antennas and Broad-Band DerivativesThereof”, Proc. IEEE, vol. 80, no. 1, January 1992). Said arrays arebased on distributing the elements that constitute it in such a mannerthat the spacing between adjacent elements and their length varyaccording to a geometric progression. Although said antennas are capableof maintaining a same radiation and impedance pattern over a broad rangeof frequencies, their application in practice is restricted to someconcrete cases due to their limitations regarding gain and size. Thusfor example, said antennas are not employed in cellular telephony basestations because they do not have sufficient gain (their gain is around10 dBi when the usual requirement is for about 17 dBi for suchapplication), they usually have linear polarisation whilst in saidenvironment antennas are required with polarisation diversity, theirpattern in the horizontal plane does not have the width necessary andtheir mechanical structure is too bulky.

The technology of individual multiband antennas is markedly moredeveloped. A multiband antenna is understood to be an antenna formed bya set of elements coupled to each other electromagnetically whichinteract with each other in order to establish the radio-electricbehaviour of the antenna, behaviour which with respect to radiation andimpedance patterns is similar in multiple frequency bands (hence thename multiband antenna). Numerous examples of multiband antennas aredescribed in the literature. In 1995 antennas of the fractal ormultifractal type were introduced (the coining of the terms fractal andmultifractal is attributable to B. B. Mandelbrot in his book The FractalGeometry of Nature, W.H. Freeman and Co. 1983), antennas which by theirgeometry have a multifrequency behaviour and, in determined cases, areduced size (C. Puente, R. Pous, J. Romeu, X. Garcia “Antenas Fractaleso Mulitfractales”, (Spanish patent P9501019). Subsequentlymulti-triangular antennas were introduced (Spanish patent P9800954)which could work simultaneously in the GSM 900 and GSM 1800 bands and,more recently, multilevel antennas (Patent PCT/ES99/00296), which offera clear example of how it is possible to shape the geometry of theantenna in order to achieve a multiband behaviour.

The present invention describes how multiband antennas can be combinedin order to obtain an array that works simultaneously in severalfrequency bands.

A Multiband Interleaved Array (MIA) consists of an array of antennaswhich has the particularity of being capable of working simultaneouslyin various frequency bands. This is achieved by means of using multibandantennas in strategic positions of the array. The disposition of theelements that constitute the MIA is obtained from the juxtaposition ofconventional mono-band arrays, employing as many mono-band arrays asfrequency bands that it is wished to incorporate in the MultibandInterleaved Array. In those positions in which one or various elementsoriginating in the conventional mono-band arrays coincide, a singlemultiband antenna (element) shall be employed which coverssimultaneously the different bands. In the remaining non-concurrentpositions, it can be chosen to employ also the same multiband antenna orelse recur to a conventional mono-band antenna which works at thepertinent frequency. The excitation at one or various frequencies ofeach element of the array depends therefore on the position of theelement in the array and is controlled by means of the signaldistribution network.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics expounded in the foregoing, are presented ingraphical form making use of the figures in the drawings attached, inwhich is shown by way of a purely illustrative and not restrictiveexample, a preferred form of embodiment. In said drawings:

FIG. 1 shows the position of the elements of two classic mono-bandarrays which work at frequencies f and f/2 respectively, and thedisposition of elements in a multiband interleaved array, which has adual frequency behaviour (at frequencies f and f/2), working in the samemanner as classic arrays but with a smaller total number of elements.

FIG. 2 shows another particular example of multiband interleaved arraybut with three frequencies in this case, and the respective threeclassic mono-band arrays which constitute it. It is a matter ofextending the case of FIG. 1 to 3 frequencies f, f/2 and f/4.

FIG. 3 shows another particular example of multiband interleaved array,in which the different working frequencies are not separated by the samescale factor. It is a matter of extending the case of FIGS. 1 and 2 to 3frequencies f, f/2 and f/3.

FIG. 4 shows a further particular example of multiband interleavedarray, in which the different working frequencies are not separated bythe same scale factor. It is a matter of extending the case of FIG. 3 to3 frequencies f, f/3 and f/4.

FIG. 5 shows a multiband interleaved array configuration which requiresa repositioning of the elements to obtain frequencies that do notcorrespond to an integer factor of the highest frequency. In thisparticular example the frequencies f, f/2 and f/2,33 have been chosen.

FIG. 6 shows the extension of the design of an MIA to thetwo-dimensional or three-dimensional case, specifically, an extension ofthe example of FIG. 1 to two dimensions.

FIG. 7 shows one of the preferred of operating modes (AEM1). It is amatter of an MIA in which the multiband elements are multi-triangularelements. The array works simultaneously at dual frequencies, forexample in the GSM 900 and GSM 1800 bands.

FIG. 8 shows another of the preferred operating modes (AEM2). It is amatter of an MIA in which the multiband elements are multilevelelements. The array works simultaneously at dual frequencies, forexample in the GSM 900 and GSM 1800 bands.

FIG. 9 shows another of the preferred operating modes (AEM3). It is amatter of an MIA in which the multiband elements are multilevelelements. The configuration is similar to that of FIG. 8 (AEM2 mode),the difference being that the new disposition permits the total width ofthe antenna to be reduced.

FIG. 10 shows another example of multiband antenna which can be employedin MIAs. It is a matter of a stacked patch antenna, which in thisspecific example works at two dual frequencies (for example, GSM 900 andGSM 1800).

FIG. 11 shows the disposition of said patches in the MIA type array(AEM4 configuration). Observe that, in contrast to the previous cases,in this case multiband antennas are employed only in those positionswhere it is strictly necessary; in the remainder mono-band elements areemployed the radiation pattern of which is sufficiently like that of themultiband element in the pertinent band.

FIG. 12 shows another configuration (AEM5), in which the elements havebeen rotated through 45° in order to facilitate the procurement ofdouble polarisation at +45° or −45°.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

In making the detailed description that follows of the preferredembodiment of the present invention, reference shall constantly be madeto the figures of the drawings, throughout which use has been made ofthe same numerical references for the same or similar parts.

A multiband interleaved array (MIA) is constituted by the juxtapositionof various conventional mono-band arrays. The conventional antennaarrays usually have a mono-band behaviour (that is, they work within arelatively small frequency range, typically of the order of 10% about acentre frequency) and this is not only because the elements (antennas)that constitute it have a mono-band behaviour, but also because thephysical spacing between elements conditions the working wavelength.Typically, the conventional mono-band arrays are designed with a spacingbetween elements of around a half-wavelength, spacing which may beincreased in some configurations in order to enhance directivity, thoughit is usually kept below one wavelength to avoid the appearance ofdiffraction lobes.

This purely geometric restriction (the magnitude of the wavelengthconditions the geometry of the elements of the array and their relativespacing) signifies a major drawback in those environments andcommunication systems in which various frequency bands have to beemployed simultaneously. A clear example is the GSM cellular mobiletelephony system. Initially located in the 900 MHz band, the GSM systemhas turned into one of the most widespread on a world scale. The successof the system and the spectacular growth in demand for this type ofservice has led to the cellular mobile telephony operators expanding itsservice into a new band, the 1800 MHz band, in order to provide coveragefor a greater customer base. Making use of classic mono-band antennatechnology, the operators have to duplicate their antenna network inorder to provide coverage simultaneously to GSM 900 and GSM 1800. Usinga single MIA specially designed for the system (like that described inthe particular cases of FIGS. 7 through 12), the operators reduce thecost of their network of base stations, the time to expand into the newband and the visual and environmental impact of their installations(through the simplification of the overall radiating structure).

It is important to point out that the scenario which has just beenoutlined above deals only with one particular example of a type of MIAand its application; as may well be gauged by anyone familiar with thesubject, in no way are the MIAs which are described in the presentinvention restricted to said specific configuration and can easily beadapted to other frequencies and applications.

The multiband interleaved arrays base their operation on the physicaldisposition of the antennas which constitute them and on the particulartype of element that is employed in some strategic positions of thearray.

The positions of the elements in an MIA are determined from thepositions of the elements in as many mono-band arrays as there arefrequencies or frequency bands required. The design of the array is, inthat sense, equal to that of the mono-band arrays insomuch as it ispossible to choose the current weighting for each element, in order toshape the radiation pattern according to the needs of each application.The configuration of the MIA is obtained from the juxtaposition of thepositions of the different mono-band arrays. Naturally, suchjuxtaposition proves difficult to implement in practice in thosepositions in which various antennas of the different arrays coincide;the solution proposed in this invention rests in the use of a multibandantenna (for example of the fractal, multi-triangular, multi-level, etc.type) which covers all the frequencies associated with its position.

A basic and particular example of how to arrange the elements in an MIAis described in FIG. 1. In the columns of the FIGS. (1.1) and (1.2) twoconventional mono-band arrays are shown in which the positions of theelements (indicated by the black circles and the circumferencesrespectively) are chosen in such a manner that the spacing betweenelements is typically less than the working wavelength. Thus, taking asreference the working frequency f of the array (1.1), the array (1.2)would work at a frequency f/2 as the elements have a spacing double thatof the previous case. In FIG. (1.3) the disposition is shown of theelements in the MIA which is capable of working simultaneously on thefrequencies f and f/2 conserving basically the same facilities as thetwo arrays (1.1) and (1.2). In the positions in which elements of thetwo conventional arrays (indicated in FIG. (1.3) by means of blackcircles located at the centre of a circumference) coincide, a multibandantenna is employed capable of working in the same manner (sameimpedance and pattern) on the frequencies (1.1) and (1.2). The remainingnot common elements (indicated either by a black circle, or by acircumference) can be implemented either by means of the same multibandelement employed in the common positions (and selecting the workingfrequency by means of the signal distribution network of the array), orby employing conventional mono-band elements. In this example the array(1.3) has a dual behaviour frequency-wise (at frequencies f and f/2),working in the same manner as the arrays (1.1) and (1.2) but with asmaller total number of elements (12 instead of 16).

Multiple examples of multiband antennas are already described in thestate of the art. Antennas with fractal geometry, multi-triangularantennas, multi-level antennas even stacked patch antennas are someexamples of antennas capable of working in like manner in multiplefrequency bands. These, and other multiband elements can be employed inthe positions of the MIAs in which elements of various mono-band arrayscome together.

In the following figures other MIA configurations are shown, based onthe same inventive concept, though having the disposition of theelements adapted to other frequencies. In FIG. 2 the configurationdescribed is that of a tri-band MIA working at frequencies f, f/2 andf/4. The disposition of elements in the three classic mono-band arraysat the frequencies f, f/2 and f/4 is illustrated in the FIGS. (2.1),(2.2) and (2.3) by means of black circles, circumferences and squaresrespectively. The position of the elements of the MIA is determined fromthe configuration of the three mono-band arrays designed for each one ofthe three frequencies. The three arrays come together in the MIA that isshown in FIG. (2.4). In those positions where elements of the threearrays would come together (indicated in the drawing by thejuxtaposition of the different geometric figures identifying each array)use is made of a multiband element. The three-frequency array of FIG.(2.4) behaves in the same manner as the three arrays (2.1), (2.2) and(2.3) at their respective working frequencies, but employing only 13elements instead of the 21 required in the total of the three mono-bandarrays.

FIGS. 3, 4 and 5 describe, by way of example and not restrictively, thedesign of other MIAs based on the same principle though at otherfrequencies. In the first two cases the frequencies employed are integermultiples of a fundamental frequency; in the case of FIG. 5 the ratiobetween frequencies is not restricted to any particular rule, though itsupposes an example of array in which the frequencies the GSM 900, GSM1800 and UMTS services can be combined.

Specifically, FIG. 3 illustrates another particular example of multibandinterleaved array, in which the different working frequencies are notseparated by the same scale factor. It concerns the extension of thecase of FIGS. 1 and 2 to 3 frequencies f, f/2 and f/3. The dispositionof elements of the three classic mono-band arrays at the frequencies f,f/2 and f/3 is shown in FIGS. (3.1), (3.2) and (3.3) by means of blackcircles, circumferences and squares respectively. The column of FIG.(3.4) shows the disposition of elements in the tri-band interleavedarray. In those positions in which elements of the three arrays cometogether (indicated in the drawing by the juxtaposition of the differentgeometric figures identifying each array), use is made of a multibandelement; the same strategy is followed in those positions in whichelements of two arrays coincide: use should be made of a multibandelement capable of covering the frequencies pertinent to its position,preferentially the same element as that used in the remaining positions,selecting those frequencies which are necessary by means of the feedernetwork. Notice that as the three-frequency array of FIG. (3.4) behavesin the same manner as the three arrays (3.1), (3.2) and (3.3) at theirrespective working frequencies, but employing only 12 elements insteadof the 21 required in the total of the three mono-band arrays.

FIG. 4 illustrates a new particular example of multiband interleavedarray, in which the different working frequencies are not separated bythe same scale factor. It concerns the extension of the case of FIG. 3to 3 frequencies f, f/3 and f/4. The disposition of elements of thethree classic mono-band arrays at the frequencies f, f/3 and f/4 areshown in FIGS. (4.1), (4.2) and (4.3) by means of black circles,circumferences and squares respectively. The column of FIG. (4.4) showsthe disposition of elements in the tri-band interleaved array. In thosepositions where elements of the three arrays would come together(indicated in the drawing by the juxtaposition of the differentgeometric figures identifying each array), use is made of a multibandelement. The three-frequency array of FIG. (4.4) behaves in the samemanner as the three arrays (4.1), (4.2) and (4.3) at their respectiveworking frequencies, but employing only 15 elements instead of the 24required in the total of the three mono-band arrays.

It is convenient to re-emphasis that in the particular cases of FIGS. 3and 4 the arrays can work at 3 frequencies simultaneously. Thedisposition of elements is such that the three frequencies do not alwayscoincide in all the elements; nonetheless, by employing a tri-bandantenna in those positions and selecting the working frequencies forexample by means of a conventional frequency-selective network, it ispossible to implement the MIA.

In some configurations of multiband interleaved array, especially inthose in which the different frequencies do not correspond to anintegral factor of the highest frequency 1, it is required that theelements be repositioned, as in FIG. 5. In this particular example thefrequencies f, f/2 and f/2,33 have been chosen. The disposition ofelements of the three classic mono-band arrays at the frequencies f, f/2and f/2,33 is represented in FIGS. (5.1), (5.2) and (5.3) by means ofblack circles, circumferences and squares respectively. The column ofFIG. (5.4) shows what would be the disposition of elements in thetri-band interleaved array according to the same plan as in the previousexamples. Notice how in this case the ratio of frequencies involves thecollation of elements at intermediate positions which make its practicalimplementation difficult. The solution to be adopted in this caseconsists in displacing the position of the element of the array thatworks at the lowest frequency (indicated by arrows) until it coincideswith another element (that nearest) of the highest frequency array; thenthe two or more coincident elements in the new position are replacedwith a multiband element. An example of the final configuration once theelements have been repositioned, is shown in FIG. (5.5). It is importantthat the element displaced be preferentially that of the lowestfrequency array, in this way the relative displacement in terms of theworking wavelength is the least possible and the appearance of secondaryor diffraction lobes is reduced to the minimum.

FIG. 6 illustrates how the configuration MIAs is not limited to thelinear (one-dimensional) case, but it also includes arrays in 2 and 3dimensions (2D and 3D). The procedure for distributing the elements ofthe array in the 2D and 3D cases is the same, replacing also thedifferent coincident elements with a single multiband antenna.

More examples of particular configurations of MIAs are described below.In the five examples described, various designs are presented for GSM900 and GSM 1800 systems (890 MHz-960 MHz and 1710 MHz-1880 MHz bands).It is a question of antennas for cellular telephony base stations, whichpresent basically the same radiofrequency behaviour in both bands; byemploying such versions of MIA antenna the operators reduce the numberof antennas installed to one half, minimising the cost and environmentalimpact of their base stations.

AEM1 Mode

The AEM1 configuration, represented in FIG. 7, is based on the use ofGSM 900 and GSM 1800 multi-triangular elements. The array is obtained byinterleaving two conventional mono-band arrays with spacing betweenelements less than one wavelength ( ) in the pertinent band (typically aspacing is chosen less than 0.9 in order to minimise the appearance ofthe diffraction lobe in the end-fire direction). The original arrays canhave 8 or 10 elements, depending on the gain required by the operator.The juxtaposition of both arrays in a single MIA is achieved in thiscase by employing dual multi-triangular elements. Such elementsincorporate two excitation points (one for each band), which allows theworking band to be selected according to their position in the array. InFIG. 7 the position of the elements is shown, as well as their workingfrequencies. The elements shown in white indicate operation in the GSM900 band; the elements shown in black indicate operation in the GSM 1800band and the elements marked in black in the lower triangle and in whitein their two upper triangles indicate simultaneous operation in bothbands. Precisely the simultaneous operation in both bands via a singlemultiband element (the multi-triangular element) in such positions ofthe array (those positions at which those of the original mono-bandarrays coincide), is one of the main characteristic features of the MIAinvention.

The manner of feeding the elements of the AEM1 array is notcharacteristic of the invention of the MIAs and recourse may be had toany conventionally known system. In particular and given that themulti-triangular elements are excited at two different points, it ispossible to make use of an independent distribution network for eachband. Another alternative consists in employing a broadband or dual banddistribution network, by coupling a combiner/diplexer whichinterconnects the network and the two excitation points of themulti-triangular antenna.

Finally, the antenna may therefore come with two input/output connectors(one for each band), or combined in a single connector by means of acombiner/diplexer network.

AEM2 Mode

This particular configuration of AEM2, shown in FIG. 8, is based on amultilevel antenna which acts as a multiband element. In addition toworking simultaneously in the GSM 900 and GSM 1800 bands, the antennahas also double linear polarisation at +45° and −45° with respect to thelongitudinal axis of the array. The fact that the antenna has doublepolarisation signifies an additional advantage for the cellulartelephony operator, since in this manner he can implement a diversitysystem which minimises the effect of fading by multipath propagation.The multilevel element which is described in FIG. 8 is more suitablethan the multi-triangular element described previously since the elementitself has a linear polarisation at +45° in GSM 900 and at −45° in GSM1800.

The array is obtained by interleaving two conventional mono-band arrayswith spacing between elements less than one wavelength ( ) in thepertinent band (typically a spacing less than 0.9 is chosen in order tominimise the appearance of the diffraction lobe in the end-firedirection). The original arrays can have 8 or 10 elements depending onthe gain required by the operator. The juxtaposition of both arrays in asingle MIA is achieved in this case by employing in-band dual multilevelelements. Such elements incorporate two points of excitation (one foreach band), which permits the working band to be selected according totheir position in the array. In FIG. 8 the position of the elements isshown, as well as their working frequencies. The elements shown in whiteindicate operation in the GSM 900 band; the elements shown in blackindicate operation in the GSM 1800 band and the elements marked in blackin their lower triangle and in white in the upper triangles indicatesimultaneous operation in both bands. Precisely the simultaneousoperation in both bands via a single multiband element (the multilevelelement) in such positions of the array (those positions in which thoseof the original mono-band arrays coincide), is one of the maincharacteristic features of the MIA invention.

It is possible to achieve double polarisation on a basis of exciting themultilevel element at various points on its surface, nonetheless inorder to augment the isolation between connectors of differentpolarisation, it is chosen in the example described to implement adouble column to separate the +45° polarization (left-hand column) fromthat of −45° (right-hand column). To increase the isolation betweenbands, it is even possible to interchange the polarisation inclinationin the columns of the array in one of the bands (for example in DCS).

The manner of feeding the elements of the array AEM2 is notcharacteristic of the invention of the MIAs and recourse can be had toany conventionally known system. In particular and given that themulti-triangular elements are excited at two different points, it ispossible to make use of an independent distribution network for eachband and polarisation. Another alternative consists in employing abroadband or dual band distribution network, by coupling acombiner/diplexer which interconnects the network and the two excitationpoints of the multilevel antenna. The antenna may then come with fourinput/output connectors (one for each band and polarisation), or elsecombined in only two connectors (one for each independent polarisation)by means of combiner/diplexer network in each polarisation.

AEM3 Mode

The AEM3 configuration, as shown in FIG. 9, is very similar to the AEM2(the position of the multilevel elements and the type of element itselfis the same as in the previous case), with the difference that theright-hand column is reversed with respect to that on the left. In thismanner an antenna with dual band and polarisation is obtained, the totalwidth of the antenna being reduced with respect to the previous case (inthis particular example the width is reduced by about 10%). In order toincrease the isolation between the columns of double polarisation it isconvenient that oblique fins be inserted between contiguous elements. Inthat case, lateral fins are also incorporated in all the elements whichwork in GSM 1800, fins which contribute to narrowing the radiation beamin the horizontal plane (plane at right angles to the longitudinal axisof the array).

Nor is the signal distribution system especially characteristic of theMIA configuration and the same system can be used as in the previouscase.

AEM4 Mode

Another example of multiband interleaved array is that termed hereinAEM4 and which is shown in schematic form in FIG. 11. In this case, themultiband element is a stacked square patch antenna (FIG. 10), though itis obvious for anyone familiar with the subject that patches of othershapes could be employed. Square- or circular-shaped types are preferredin the event that is wished to work with double polarisation. In theexample of FIG. 10 the particular case is described of square patches.

The lower patch is of appropriate size for its resonant frequency(associated typically with the patch fundamental mode) to coincide withthe lower band (GSM 900 in this specific case); moreover, this patchacts in turn as ground plane of the upper patch. The latter is of a sizesuch that its resonance is centered in the upper band (GSM 1800). Theelements of the array are mounted on a metallic or metal-coated surfacewhich acts as ground plane for all the elements of the array. The feedersystem is preferentially of the coaxial type, a cable being employed forthe lower patch and band and another for the upper patch and band. Theexcitation points are collated on the bisectors of the patches (forexample, the approximate excitation points are marked by means ofcircles on the plan view of the antenna) if vertical or horizontalpolarisation is desired, or on the diagonals if, on the other hand,linear polarisation inclined at 45° is desired. In the event it isdesired that the array work with double polarisation, each of thepatches is excited additionally on the bisector or diagonal opposite(orthogonal) to the first.

The feeding of the elements of the array AEM4 is not characteristic ofthe invention of the MIAs and recourse can be had to any conventionallyknown system. In particular and given that the stacked patch antenna isexcited at two different points, it is possible to make use of anindependent distribution network for each band and polarisation. Anotheralternative consists in employing a broadband or dual band distributionnetwork, by coupling a combiner/diplexer which interconnects the networkand the two excitation points of the multilevel antenna.

The antenna may then come with four input/output connectors (one foreach band and polarisation), or else combined in only two connectors(one for each independent polarisation) by means of a combiner/diplexernetwork in each polarisation.

AEM5 Mode

The AEM5 configuration, as shown in FIG. 12, adopts the same approach asthe AEM4, though all the elements are rotated through 45° in the planeof the antenna. In this manner the radiation pattern is modified in thehorizontal plane, in addition to rotating the polarization through 45°.

It is of interest to point out that both in the AEM4 configuration andin the AEM5, the multiband element constituted by the stacked patches isreally only strictly necessary in those strategic positions in whichelements originating in the conventional mono-band arrays coincide. Inthe remaining positions, it shall be possible to employ indistinctlymultiband or mono-band elements that work at the frequency determinedfor its location, as long as its radiation pattern is sufficiently likethat of the stacked patch antenna in order to avoid the appearance ofdiffraction lobes.

It is not deemed necessary to extend further the content of thisdescription in order that an expert in the subject can comprehend itsscope and the benefits arising from the invention, as well as developand implement in practice the object thereof.

Notwithstanding, it must be understood that the invention has beendescribed according to a preferred embodiment thereof, for which reasonit may be susceptible to modifications without this implying anyalteration to its basis, it being possible that such modificationsaffect, in particular, the form, the size and/or the materials ofmanufacture.

The invention claimed is:
 1. An antenna array comprising: a ground planelayer; a first set of antenna elements arranged on the ground planelayer and being configured to provide operation of the antenna array inat least three frequency bands respectively corresponding to threecellular frequency bands; a second set of antenna elements arranged onthe ground layer and being configured to provide operation of theantenna array in two of the three frequency bands; the first set ofantenna elements and the second set of antenna elements aresubstantially arranged along a longitudinal direction of the antennaarray; and the first set of antenna elements and the second set ofantenna elements are arranged on alternating positions along thelongitudinal direction, wherein a ratio of a spacing between antennaelements of the first set to a wavelength of a first frequency band ofthe three frequency bands is substantially half of a ratio of a spacingbetween antenna elements of the second set to a wavelength of a secondfrequency band of the three frequency bands.
 2. The antenna array ofclaim 1, further comprising: a first distribution network configured toexcite the first set of antenna elements, and a second distributionnetwork configured to excite the antenna elements providing operation ofthe antenna array at the second band and a third frequency band of thethree frequency bands.
 3. The antenna array of claim 1, wherein thefirst set of antenna elements comprises a plurality of single multibandantenna elements, and each of the single multiband antenna elementscomprises a plurality of electromagnetically coupled portions that areconfigured to interact with each other.
 4. The antenna array of claim 1,wherein a ratio between a frequency of the third frequency band and afrequency of the second frequency band is less than 1.5.
 5. The antennaarray of claim 1, wherein a frequency for the first frequency band issituated around 900 MHz, a frequency for the second frequency band issituated around 1800 MHz, and a frequency for the third frequency bandis situated around 2100 MHz.
 6. The antenna array of claim 1, whereinthe three frequency bands are not separated by the same scale factor. 7.A communication system comprising: a network of base stations comprisinga plurality of base stations, at least some of the plurality of basestations comprising the antenna array of claim
 1. 8. An antenna arraycomprising: a ground plane layer; a first plurality of antenna elementsarranged on the ground plane and being configured to provide operationof the antenna array in at least first and second frequency bandsrespectively corresponding to two cellular frequency bands, the firstand second frequency bands being non-overlapping frequency bands; and asecond plurality of antenna elements arranged on the ground plane layerand being configured to provide operation of the antenna array in thesecond frequency band, wherein the first plurality of antenna elementsand the second plurality of antenna elements are substantially arrangedalong a longitudinal direction of the antenna array; and a ratio of aspacing between antenna elements providing operation at the firstfrequency band to an operating wavelength of the first frequency band issubstantially the same as a ratio of a spacing between antenna elementsproviding operation at the second frequency band to an operatingwavelength of the second frequency band.
 9. The antenna array of claim8, wherein the antenna elements of the first plurality and the antennaelements of the second plurality are arranged in alternating positionsalong the longitudinal direction of the antenna array.
 10. The antennaarray of claim 9, wherein a ratio between an operating frequency of thesecond frequency band and an operating frequency of the first frequencyband is greater than two.
 11. The antenna array of claim 8, wherein eachantenna element of the first plurality of antenna elements comprises aplurality of electromagnetically coupled portions configured to interactwith each other.
 12. The antenna array of claim 11, further comprising afirst distribution network configured to excite the first plurality ofantenna elements, and a second distribution network configured to excitethe antenna elements providing operation at the second frequency band.13. A communication system comprising: a network of base stationscomprising a plurality of base stations, at least some of the pluralityof base stations comprising the antenna array of claim
 8. 14. An antennaarray comprising: a ground plane layer; a plurality of antenna elementsarranged on the ground plane layer along a longitudinal direction of theantenna array; a first distribution network configured to excite theplurality of antenna elements for a first polarization; and a seconddistribution network configured to excite the plurality of antennaelements for a second polarization, the first and second polarizationsbeing orthogonal polarizations, wherein: the plurality of antennaelements are configured to provide operation of the antenna array inthree frequency bands respectively associated with three cellularfrequency bands; the highest frequency of a first frequency band of thethree frequency bands is less than the lowest frequency of a secondfrequency band of the three frequency bands and the lowest frequency ofa third frequency band of the three frequency bands is greater than thehighest frequency of the second frequency band; a ratio between afrequency of the third frequency band and a frequency of the firstfrequency band is less than 1.5; a spacing between the antenna elementsof the plurality of antenna elements is less than a wavelength of thelowest operating frequency of the first frequency band; and a spacingbetween the antenna elements of the plurality of antenna elements isgreater than a half wavelength of the highest frequency of the thirdfrequency band.
 15. The antenna array of claim 14, wherein a firstspacing between a first pair of adjacent antenna elements of theplurality of antenna elements is different from a second spacing betweena second pair of adjacent antenna elements of the plurality of antennaelements.
 16. The antenna array of claim 14, wherein any operatingfrequencies of the third frequency band does not correspond to aninteger factor of an operating frequency of the first frequency band.17. The antenna array of claim 14, wherein the three frequency bands arenot separated by the same scale factor.
 18. The antenna array of claim14, wherein the antenna elements of the plurality of antenna elementscomprises patch antennas.
 19. A communication system comprising: anetwork of base stations comprising a plurality of base stations, atleast some of the plurality of base stations comprising the antennaarray according to claim 14.